1. Field of the Invention
The present invention relates generally to a button setting machine having an optical position indicator for indicating a correct location in alignment between a punch and a die of the button setting machine, and more particularly to a method and apparatus for protecting the optical position indicator from collision with the punch.
2. Description of the Prior Art
Optical position indicators composed of light projectors are incorporated in button setting machines for indicating an accurate position on the garment fabric where upper and lower elements of a fastener, such as a stud button for denim jeans, are to be attached by and between a punch and a die of the button setting machine. For an accurate positioning, it is desirable that the light projector is disposed in a position directly below the punch. To this end, the light projector is mounted on a reciprocable pusher which is constructed to commence retracting movement of the light projector in synchronism with the downward movement of the punch. In order to prevent accidental interference or collision between the punch and the light projector, the retraction of the light projector from the path of movement of the punch must be completed before the punch is lowered to the level of the light projector. This means that a relatively large space must be provided between a lower end of the punch and the light projector. With this large spacing, the punch has a long stroke and hence the button setting machine becomes large as a whole. Another drawback resulting from the large spacing between the punch and the light projector is that a perfect synchronization between the downward movement of the punch and the retracting movement of the light projector is difficult to maintain and the button setting machine is complicated in construction.
One prior attempt proposed to overcome the foregoing difficulties includes a light projector such as disclosed in Japanese Utility Model Laid-open Publication No. 63-183227. The disclosed light projector is pivotably connected to a holder member secured to a horizontally reciprocable pusher and is urged upwardly by a resilient member. With this construction, when the punch while being driven downwardly interferes with or collides with the light projector, the light projector pivots downwardly away from the path of movement of the punch against the bias of the resilient member.
The downwardly pivotable light projector is simple in construction however it is likely to be damaged by impact forces applied thereto each time the punch collides with the light projector. Furthermore, a repeated collision with the punch gradually deteriorates the positioning accuracy of the light projector.